Amplifier



April 2, 1935. w. w. EITEL AMPLIFIER Filed Dec. 9, 1932 2 Sheets-Sheet lI O O INVENTOR.

WILL/AM W. E/TEL.

ATTORNEY April 2, 1935.

w. w. EITEL 1,996,507

AMPLIFIER Filed Dec. 9, 1932 2 Sheets-Sheet 2 F z'g.5

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Wm hunk INVENTOR WILL/AM WI E/TEL.

ATTORNEY Patented Apr. 2, 1935 omrro STATES Application December '9,1932, Serial No. 646,469

9 Claims.

My invention relates to .amplifiers, and particularly to amplifiersdesigned for operation at the higher radio frequencies.

Among the objects .of my invention are: To

c provide .an amplifier capable of providing large amounts of outputpower; to provide an amplifier having extremely low output impedance andrelatively high input impedance; to provide an amplifier wherein theoutput circuit is substantially without effect upon the input circuit;to provide an amplifier which may .be used almost at the point ofself-oscillation without afiecting materially the input constants of theamplifier; and to provide an amplifier wherein the type of vacuum tubecharacterized by a plate-like control electrode mounted in opposition toa similarly formed output electrode maybe utilized to provide largepower outputs at relatively ,high efficiency.

Other objects of my invention will be apparent or will he specificallypointed out in the description forming a part of this specification, butI do not. limit myself to the embodiment of my invention hereindescribed, as various forms may be adopted within the scope of theclaims.

Referring to the drawings;

-Figure 1 is a view, partly in elevation and partly in section, of atube adapted for usein the amplifier of this invention.

Fi u 2 is a transverse section of the tube shown in Figure 1, the planeoi projection being on the line '2.2 of the first figure.

Figure 3 is a fragmentary sectional view of the tube, taken on the line3?3 of Figure 2, and showing the auxiliary accelerating electrode.

Figure 4 is .a circuit diagram of the amplifier.

Figure 5 is a similar diagram showing a modified form of the amplifier.

The invention involves the use of a vacuum" tube having the usualcathode, anode, and control electrode, and, in addition, an acceleratingelectrode whose function is to increase the mutual conductance ortransductance of the tube by increasing the velocity of electronsleaving the fila-' 45 ment, and neutralizing or partially neutralizingthe space charge thereof. Such an electrode, it will be seen, has acertain degree of control over the space current, and this control is inthe same sense as that of the control electrode, i. e., a negative swingin potential of the control electrode decreases the space current, whileapositive swing increases this current.

The input circuit of the amplifier is connected to the control electrodein the usual manner, while the anode connects to the outpu c rc case bya band or clamp l2 surrounding a 're- I entrant stem M at one-end of thetube.

The accelerating electrode is coupled to the anode in such a manner asto augment the effect of the control electrode on the space current; i.e., so that adecrease in space current impresses a less positivepotential upon the accelerating eIectrode. In this mannertheeffectiveItransductance of the tube is very greatly increased, as isthe effective amplification constant,.butthere is no reaction upon theinput circuit of the device as is the case where regeneration orfeedback is used. It is therefore possible greatly to increase theamplification and power output of the tube without introducing thedistortion present inregenerativ vamplifiers. Furthermore, since theaccelerating electrode is operatedat d5 a'positive potential, the outputimpedance of the tube may be made. very low, and, large effective poweroutput may be obtained even with'relatively low amplification factors.j.

In order to take fluIIestadvantage-oi the latter feature of the device,it is preferable that the tube used be .of the type wherein-a plate-likecontrol electrode is positioned on oneside of .a

filamentary cathode, while the anode ,or. platelis' positioned on theother side and at .a greaterdistance therefrom.. A prefer-red form ofsuch a tube is illustrated in Figures 1, 2 and 3, wherein an envelope Iis provided with side stems 2 through which are sealed support rods 4for holding the plate-like control electrode 5. 0n the opposite side ofthe envelopeia similar set of side stems 6 and support rods "I hold theanode 9. Between the control electrode andithe anode the filament i0 ispositioned, the filament being much more. closely adjacent/the controlelectrodethan the anode.

The acceleratingelectrode, which is of reticulated or grid-like form ispositioned between the anode and the filament, being supported-in this Atube of the character shown, but without the accelerating electrode, iscapable of handling relatively large amounts of power, but is limited asto amplification. Thus acommerciallybuilt tube of this type will have anamplification constant of perhaps three or four, but its outputimpedance will be lowo-f the order of 500 or 600 ohms.

The addition of the accelerating electrode H, which should be operatedat a potential positive with respect to the cathode, has two efiects.First, it greatly decreases the efiective capacity between thecontrolelectrode and the anode,'thus reducing the reaction between the outputand input circuits of the device, and second, it still further decreasesthe output impedance of the device.

The application of the tube to the amplifier of my invention is shownschematically in Figure 4. An input circuit comprising leads 2E] and 2|connects to the cathode l0 and control electrode 5. The anode or plate 9is connected toan output circuit comprising an inductor 22 tuned by acondenser 24, a tap 25 on the inductor being connected to ground througha by-pass condenser 26. Anode current is supplied to the output circuitfrom a battery or other suitable source 21, the accelerating electrode Hbeing connected to an intermediate point on this battery through achoke-coil 29. The electrode II is also connected to the terminal of thetuned output circuit opposite that to which the anode-9 is connected,through a blocking condenser 30.

The operation of the circuit is as follows: When an impulse applied tothe input circuit swings the control electrode negative, the spacecurrent between cathode and anode is decreased, swinging the anodepositive in accordance with the well known functioning of tubes of thistype. The decrease in current through the inductor 22 induces a negativepotential at the end of the coil opposite to the anode connection, andthis potential is applied to the accelerating electrode ll, superposedupon the constant potential applied thereto by the battery 21 throughthe chokecoil 29. The decrease in positive potential applied to thiselectrode serves further to decrease the space current, therebytending-to increase the positive potential on the anode and augment theeffect produced thereon by the control electrode. A positive potentialapplied to the control electrode 5 has the opposite effect, swinging theanode negative and the accelerating electrode positive. 7

There is, however, no reaction produced on the input circuit by thisaction. Not only is the control electrode shielded from the plate by theaccelerating electrode, but since the control electrode actuallyswingsin the opposite sense to the swing in plate potential, this has areverse effect to that of the plate, and completely cancelling out anytendency toward capacity feedback into the input circuit. ,7

The amount by which the auxiliary electrode augments the effect of'thecontrol electrode may be controlled by varying the point at which thetap 25 connects to the inductance 22. It is possible under certaincircumstances to increase this eifect until the circuit becomesself-oscillatory,

although this point is not reached as readily as it would be were theaccelerating electrode operated at a mean negative potential withrespect to the filament. At points below self-oscillation, however,there is very much less tendency to produce distortion through theeffect of this augmentation than is the case where feedback orregeneration is used. It is to be noted that the entire circuit stillremains primarily under the control of the control electrode 5, and thatthere is no feedback to this circuit. Accordingly there is no effectivereduction of resistance in this circuit, and hence there is lesstendency toward excessive amplification on a single frequency than incircuits in which feedbacks occur. The amplifier is therefore applicableto audio frequency circuits or other circuits where tuning isundesirable, the only difierence in such applications being that thetuning condenser 24 isomitted.

Power may be withdrawn from the output circuit either through the leads3| and 32, or by making coil 22 the primary of a transformer.

A slight modification of the circuit is shown in Figure 5. In thisinstance the connections, although differently arranged in the diagram,are essentially the same as in Figure 4-, the diiference being that aneutralizing condenser 35 connects between the electrode H and thecontrol electrode 5. This arrangement is applicable for use with tubeswherein the shielding effect and neutralizing effect of the acceleratingelectrode II are not sufiicient completely to counteract capacitycoupling between the anode 9 and the con- 'trol electrode 5.

since this results in minimum impedance in' the 5 tubes. Where suchtubes are used, however, the effective-impedance of the tube will bemuch greater than in the cases described above.

In practice I have found that the connection as shown will raise theeffective amplification constant of a tube of this class approximatelythree-fold, and at the same time will reducethe elfective a-c. impedanceof the tube approximately to one-half. It will therefore be apparentthat the effectiveness of the amplifier, as measured by the watts outputdivided by the watts input, is greatly increased, as is the total'amountof power which the amplifier will deliver.

I claim:

1. The combination with a thermionic tube having a cathode, a plateelectrode on one side of said cathode, a control electrode on the otherside of said cathode, and an accelerating'electrode between said cathodeand said anode, of means for applying impulses to said controlelectrode, and means for coupling said accelerating electrode to saidplate electrode in such phase relationship that potential changes insaid plate electrode initiated by said control electrode are augmentedby said accelerating electrode.

2. The combination with a thermionic tube having a cathode, a plateelectrode on one side of said cathode, a control electrode on the otherside of said cathode, and an accelerating electrode between said cathodeand said anode, of an input circuit connected to said control electrode,an output circuit connected to said plate electrode, and a connectioncoupling said accelerating electrode to said plate electrode to impresson said accelerating electrode a potential of opposite sign to that onsaid plate electrode.

3. The combination with a vacuum tube having a cathode, an anode on oneside of said cathode, a control electrode on the other side of saidcathode, and an accelerating electrode between said anode and cathode,of an input circuit connected to said control electrode, an outputcircuit connected to said anode, and coupling means connecting, saidanode and said auxiliary electrode in such phase relation that voltagesderived from said output circuit afiect said accelerating electrode toaugment the efiect of said control electrode on the current flow.

4. The combination with a vacuum tube having a cathode, an anode on oneside of said cathode, a control electrode on the other side of saidcathode, and an accelerating electrode between said anode and cathode,of an input circuit connected to said control electrode, an outputcircuit connected to said anode, coupling means connecting said anodeand. said auxiliary electrode in such phase relation that voltagesderived from said output circuit affect said accelerating electrode toaugment the effect of said control electrode on the current flow, andmeans for preventing reaction between said output circuit and said inputcircuit.

5. The combinaion with a vacuum tube having a cathode, an anode on oneside of said cathode, a control electrode on the other side of saidcathode, and an accelerating electrode between said anode and cathode,of an input circuit connected to said control electrode, an outputcircuit including an impedance element connected to said anode, andcoupling means between said impedance element and said acceleratingelectrode for impressing thereon voltages of opposite phase from thevoltage on said anode.

6. The combination with a vacuum tube having a cathode, an anode on oneside of said cathode, a control electrode on the other side of saidcathode, and an accelerating electrode between said cathode and saidanode, of an input circuit connected to said control electrode, anoutput circuit connected to said anode, and means coupling saidanodeland said accelerating electrode for transferring therebetweenvoltages reversed in phase relation.

'7. The combination with a vacuum tube having a cathode, an anode on oneside of said cathode, a control electrode on the other side of saidcathode, and an accelerating electrode between said anode and cathode,of an input circuit con-- nected to said controlelectrode, and a tunedoutput circuit, one end of said tuned circuitbeing connected to saidanode and the other connected to said accelerating electrode, wherebythe potentials of said anode and said auxiliary electrode are maintainedin opposite phase relationship.

8. The combination with a vacuum tube having a cathode, an anode on oneside of said cathode, a control electrode on the other side of saidcathode, and an accelerating electrode between said anode and cathode,of an input circuit con-,1

nected to said control electrode,a tuned output circuit, one end ofsaid. tuned circuit being connected to said anode and the otherconnected to said accelerating electrode, and means for maintaining thealternating current potential of said cathode intermediate that of saidanode and accelerating electrode. 1'

9. The combination with a vacuum tube having,

accelerating electrode, and means for maintaining the mean potential ofsaid cathode negative with respect to both said anode and saidaccelerating electrode.

WILLIAM W. EITEL.

